This invention relates generally to golf balls, and more particularly to wound golf balls made with multiple threads.
Conventional golf balls can be divided into two general groups: solid balls or wound balls. The difference in play characteristics resulting from these different types of construction can be quite significant. Balls having a solid construction are generally most popular with the average recreational golfer because they provide a very durable ball while also providing maximum distance. Solid balls are generally made with a solid core, usually made of a cross linked rubber, enclosed by a cover material. Typically the solid core is made of polybutadiene which is chemically crosslinked with zinc diacrylate and/or similar crosslinking agents. In addition to one-piece solid cores, solid cores may also contain a number of outer layers, such as in a dual core golf ball. The cover is generally an ionomeric material, such as SURLYN(copyright), which is a tradename for a family of ionomer resins produced by E. I. DuPont de Nemours and Co. of Wilmington, Del. Covers are typically a single layer but may also include one or more layers, such as in a double cover having an inner and outer cover layer.
The combination of the solid core and ionomeric cover materials provide a ball that is very durable and abrasion resistant. Further, such a combination imparts a high initial velocity to the ball which results in increased distance. Because these materials are very rigid, however, solid balls can have a hard xe2x80x9cfeelxe2x80x9d when struck with a club. Likewise, due to their construction, these balls have a relatively low spin rate which provides greater distance.
At the present time, wound golf balls generally are the preferred ball for the more advanced player due to the spin and feel characteristics afforded by such a construction. Wound balls typically have either a spherical solid rubber or liquid center core, around which many yards of a tensioned elastomeric thread are wound. The wound core is then covered with a durable cover material, such as SURLYN(copyright) or similar material, or a softer cover material, such as balata or polyurethane. Wound balls are generally softer and provide more spin, which enable a skilled golfer to have more control over the ball""s flight and position. Particularly, with approach shots onto the green, the high spin rate of soft, wound balls enable the golfer to stop the ball very near its landing position.
Regardless of the form of the ball, players generally seek a golf ball that maximizes total game performance. Therefore, in an effort to meet the demands of the marketplace, manufacturers strive to produce golf balls with a wide variety of performance characteristics to meet the players individual requirements. Thus, golf ball manufacturers are continually searching for new ways in which to provide golf balls that deliver the maximum performance for golfers of all skill levels.
To make wound golf balls, manufacturers use winding machines to stretch the elastic threads to various degrees of elongation during the winding process without subjecting the threads to unnecessary incidents of breakage. Generally, as the elongation and the winding tension increases, the compression and initial velocity of the ball increases. Thus, a more resilient wound ball is produced, which is desirable.
For golf balls, the thread is typically formed by a calendar and slitting method rather than an extrusion method. The calendered thread has a rectangular cross-section, while extruded thread generally has a circular cross-section. Extruded thread was not previously used in golf ball applications, because it has not exhibited the physical properties necessary for proper performance of golf balls. An example of an extruded thread that is not used in golf balls is disclosed in U.S. Pat. No. 5,679,196 issued to Wilhelm et al. This patent discloses a thread formed of a mixture that has more than 50% natural rubber.
A number of different windings have been disclosed for use in golf balls. U.S. Pat. No. 4,473,229 to Kloppenburg et al. discloses a golf ball having a core formed of graphite fibers and windings made of graphite filaments and resins. Yarns are made with the graphite filaments and resins, and as many as four or more yarns are combined to form a final yarn used for winding. U.S. Pat. No. 5,713,801 to Aoyama discloses use of a layer of high tensile elastic modulus fibers wound about the core. The fibers have a tensile elastic modulus of at least 10,000 psi. Also, U.S. Pat. No. 5,816,939 to Hamada et al. discloses a rubber thread for winding with a tensile strength retention of xe2x89xa770%, a hysteresis loss of no more than 50%, and an elongation of 900-1400%.
Prior art wound golf balls and cores typically use polyisoprene rubber thread. The polyisoprene thread is wound onto the cores at elongations between 500-1000%. The amount of thread required for a golf ball core is dependent on the elastic modulus of the thread in the elongated state. Elongated polyisoprene thread generally has an elastic modulus between 10,000 and 20,000 psi. Further, the properties, in particular resilience, of the wound ball or core are dependent on how well the thread packs during winding. The dimensions of the thread control the packing density. Present art polyisoprene threads are typically {fraction (1/16)}-inches wide by 0.02-inches thick, measured prior to winding. However, present art polyisoprene thread is commonly produced in thicknesses between 0.014 inches and 0.024 inches.
There are some drawbacks to the conventional single-ply threads used in golf balls. The single-ply occasionally contains weak points. As a result, manufacturers of wound balls do not wind using the maximum tension or stretch the thread to the maximum elongation, because to do so would cause an excessive amount of breakage during winding. When a thread breaks during manufacturing, an operator must restart the operation. This decreases production, and is thus undesirable. The use of two-ply threads in golf balls reduces but does not eliminate this problem.
The present invention is directed to wound single and multilayer golf ball cores and golf balls. Generally, the prior art has been directed to making golf balls and cores using single-ply or two-ply polyisoprene thread. The resilience and other properties of the golf ball are dependent on how well the thread packs during winding. The present invention is directed to a golf ball that has multiple threads wound on the golf ball center simultaneously. More preferably, the present invention is directed to a golf ball that has multiple threads wound about the center simultaneously where the threads have different properties.
Preferably, the golf ball of the present invention provides a wound core of a golf ball with unique thread construction and performance characteristics through the use of at least two threads having different chemical, physical, thermal or mechanical properties. Conventional calendering and slitting, melt spinning, wet spinning, dry spinning, and polymerization spinning may be used to produce the threads. Most preferably, each of the threads wound onto the center are different from each other in some characteristic such as cross-section, composition, elongated state, physical property, or mechanical properties. Mechanical properties are, for example, resiliency, elastic modulus, and density.
The threads may be comprised of a suitable material including polyisoprene. Suitable polymers include polyether urea, such as LYCRA(copyright), polyester urea, polyester block copolymers such as HYTREL(copyright), isotactic-poly(propylene), polyethylene, polyamide, poly(oxymethylene), polyketon, poly(ethylene terephthalate) such as DACRON(copyright), poly(p-phenylene terephthalamide) such as KEVLAR((copyright), poly(acrylonitrile) such as ORLON(copyright), diaminodicyclohexylmethane and dodecanedicarboxylic acid such as QUINA(copyright). LYCRA(copyright), HYTREL(copyright), DACRON(copyright), KEVLAR(copyright), ORLON(copyright), and QUINA(copyright) are available from E. I. DuPont de Nemours and Co. of Wilmington, Del. Glass fiber and, for example, S-GLASS(copyright) from Corning Corporation can be used.
The center is wound with the threads by placing the center on a drive belt and having a support roller apply a force to maintain the center against the drive belt. As the drive belt is turned, the center is spun. Preferably, at least two threads are fed from at least one feed spool through a tension controller. The stretched threads are then fed together onto the spinning center. When the wound ball reaches the desired diameter, a sensor attached to the support roller will recognize the size and stop the drive belt from rotating thereby stopping the threads from being wound onto the center. The threads are then cut and tied, allowing the wound center to be removed from the drive belt. The threads can be fed to the center at different angles and tensions. Moreover, the wound layer of different threads could be xe2x80x9cfusedxe2x80x9d together under the pressures and temperatures of molding, allowing utilization of the characteristics of all the threads.
The inner sphere, or center, of the golf ball may be of any dimension or composition, such as a thermoset solid rubber sphere, a thermoplastic solid sphere, wood, cork, metal, or any material known to one skilled in the art of golf ball manufacture. Preferably, the solid inner sphere is comprised of a resilient polymer such as polybutadiene, natural rubber, polyisoprene, styrene-butadiene, or ethylene-propylene-diene rubber. Similarly, the inner sphere could be a liquid filled sphere or shell such as a rubber sack, a thermoplastic, or metallic shell design, in which the liquid could be of any composition or viscosity. It is also feasible to construct such a center with a void or gas center. In another embodiment, the center can be filled with a liquid, a gel, a paste, a cellular foam, or a gas. Preferably, the center outer diameter is about 0.5 to 1.5 inches. Preferably, the combination of the center and the wound layer has an outer diameter of about 1.4 to 1.62 inches.
Finally, a cover is molded around the core. The cover can have one or more layers. Any process that results in accurate and repeatable central placement of the core within the cover is acceptable. Generally, covers are applied by compression molding, injection molding or casting cover material over the core.